Fix get item out of range error (#24339) (#24943)

* raise index error when slice out of range; test=develop

* add uni test; test=develop

* fix format error; test=develop

* add comment for py::index_error; test=develop

* polish error message; test=develop

* polish error message; test=develop

Author: phlrain

paddle/fluid/pybind/imperative.cc

@@ -322,7 +322,18 @@ static void ParseIndexingSlice(framework::LoDTensor *tensor, PyObject *_index,
     if (PyCheckInteger(slice_item)) {
       // integer, PyLong_AsLong supports both int and long
       int start = static_cast<int>(PyLong_AsLong(slice_item));
+      auto s_t = start;
       start = start < 0 ? start + dim_len : start;
+      if (start >= dim_len) {
+        std::string str_error_message =
+            "The starting index " + std::to_string(s_t) +
+            " of slice is out of bounds in tensor " + std::to_string(dim) +
+            "-th axis, it shound be in the range of [" +
+            std::to_string(-dim_len) + ", " + std::to_string(dim_len) + ")";
+        // py::index_error is corresponding to IndexError in Python
+        // Used to indicate out of bounds access in __getitem__, __setitem__
+        throw py::index_error(str_error_message);
+      }
       slice_axes->push_back(dim);
       slice_starts->push_back(start);
       slice_ends->push_back(start + 1);

python/paddle/fluid/tests/unittests/test_var_base.py

@@ -181,14 +181,25 @@ def _test_slice(self):
         self.assertTrue(
             np.array_equal(local_out[15], tensor_array[::-1, ::-1, ::-1]))
 
+    def _test_for_var(self):
+        np_value = np.random.random((30, 100, 100)).astype('float32')
+        w = fluid.dygraph.to_variable(np_value)
+
+        for i, e in enumerate(w):
+            self.assertTrue(np.array_equal(e.numpy(), np_value[i]))
+
     def test_slice(self):
         with fluid.dygraph.guard():
             self._test_slice()
+            self._test_for_var()
 
             var = fluid.dygraph.to_variable(self.array)
             self.assertTrue(np.array_equal(var[1, :].numpy(), self.array[1, :]))
             self.assertTrue(np.array_equal(var[::-1].numpy(), self.array[::-1]))
 
+            with self.assertRaises(IndexError):
+                y = var[self.shape[0]]
+
     def test_var_base_to_np(self):
         with fluid.dygraph.guard():
             var = fluid.dygraph.to_variable(self.array)